This invention relates an optical isolator, and more particularly to an optical isolator provided with inner polarizers which are made in YVO.sub.4 (Yttrium Vanadate) materials.
In present day optical fiber technology, semiconductor lasers are typically used to generate and relay light signals on optical fibers. These lasers are particularly susceptible to light signal reflections, which cause a laser to become unstable and noisy. Optical isolators are used to block these reflected signals from reaching the laser. Ideally, these optical isolators transmit all of the light signals in the forward direction and block all of the signals in the reverse direction.
Of course, optical isolators do not attain ideal performance levels and improvements are constantly being sought. Furthermore, optical fiber technology has an inherently large bandwidth which has encouraged the spread of optical fiber networks. However, one factor which has slowed the use of optical fiber technology has been costs, including those for optical isolators. With an optical isolator generally required for each laser generating signal on an optical fiber, it is highly desirable that the cost of the optical isolators be lowered as much as possible.
Conventionally, polarization dependent optical isolators and polarization independent optical isolators are employed in an optical fiber system. The polarization dependent optical isolator is undesirable since it has many limitations. Conversely, the polarization independent optical isolator is widely used for it is compatible with most light sources.
There are three kinds of prior art polarization independent optical isolators. In U.S. Pat. No. 5,151,955, the disclosed optical isolator employed three birefringent crystals and two magnetic-optical devices. This is not an ideal design, for its price is too high and its beam splitting effect depends on the diameter of the light beam. Furthermore, the U.S. Patent `OPTICAL DEVICES` (U.S. Pat. No. 4,548,478) and the U.S. Patent `OPTICAL ISOLATOR` (U.S. Pat. No. 5,208,876) both employed two birefringent crystal wedges as an optical walk-off polarizer and analyzer. The above two patents also display the drawbacks of high cost and low relative refractive index difference; for they used calcite, rutile and lithium niobate as the material for the polarizer and analyzer.
The present invention solves or substantially ameliorates these problems by offering an optical isolator displaying a higher relative refractive index difference, and the benefits of with lower cost and easy manufacture.